How to input dataset with multi-value properties?
You could use scikit-learn's MultiLabelBinarizer. It's essentially the multi-label equivalent of one-hot encoding. For each movie, create a vector of zeros, where each zero is associated with a particular actor. If an actor is in that movie, change their zero to a one. In the context of a neural network, think of it as each actor having their own input neuron, which will fire only if they are in that movie.
The caveat is that to represent all actors, you'd need a rediculously long vector. In such cases, it's often sufficient to only look at the most common, say, 100 and ignore the rest. It intuitively makes sense that having a big actor who's done a lot of movies says more about the quality of a movie than whoever's playing Unimportant Bystander #3. This is actually how natural language processing represents words in the English language - take the top n and ignore the rest.